fix

lib/internal/test_runner/test.js

@@ -93,6 +93,7 @@ class Test extends AsyncResource {
       this.reporter = new TapStream();
       this.runOnlySubtests = this.only;
       this.testNumber = 0;
+      this.shouldReportSubtest = false;
     } else {
       const indent = parent.parent === null ? parent.indent :
         parent.indent + parent.indentString;
@@ -104,6 +105,7 @@ class Test extends AsyncResource {
       this.reporter = parent.reporter;
       this.runOnlySubtests = !this.only;
       this.testNumber = parent.subtests.length + 1;
+      this.shouldReportSubtest = true;
     }
 
     if (isUint32(concurrency) && concurrency !== 0) {
@@ -162,7 +164,6 @@ class Test extends AsyncResource {
   processReadySubtestRange(canSend) {
     const start = this.waitingOn;
     const end = start + this.readySubtests.size;
-    let shouldReportSubtest = this.parent !== null;
 
     for (let i = start; i < end; i++) {
       const subtest = this.readySubtests.get(i);
@@ -184,9 +185,9 @@ class Test extends AsyncResource {
         return;
       }
 
-      if (shouldReportSubtest) {
+      if (this.shouldReportSubtest) {
         this.reporter.subTest(this.indent, this.name);
-        shouldReportSubtest = false;
+        this.shouldReportSubtest = false;
       }
 
       // Report the subtest's results and remove it from the ready map.

test/message/test_runner_output.out

@@ -238,7 +238,6 @@ not ok 22 - sync throw non-error fail
       ---
       duration_ms: *
       ...
-# Subtest: level 0a
     # Subtest: level 1c
     ok 3 - level 1c
       ---